On a regular apple keyboard, you simulate <alt>-<F4>(end task) with <fn><alt><f4>. might even be the same on a macbook. If you want the taskmgr so you can forcibly quit an application, then the send keys option posted by Stacy M is one way. If the Parallels application is the front most window, then <fn><ctrl><alt><del> should also work, but you need to pianist to do that easily.